来自《耶鲁大学开放课程：基础物理 第7集 第7集》

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  v^2·r keeps on increasing;
  v^2·r 随之增加
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  so the mass enclosed is increasing,
  说明质量也在增加
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  but you don't see it.
  但你肉眼没法看出来
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  That's how you know
  于是我们发现
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  there is mass which is not visible to visible observation.
  有些质量是看不到的
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  But every galaxy seems to have this halo of dark matter.
  但每个星系都有这样一个暗物质的晕轮
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  And that's how we estimate the mass
  这样我们能估算出这份质量
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  and it beats all the known mass.
  它远远大于可见的质量
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  But you can do that using just this calculation.
  你们可以用这个方法来进行计算